POLK

Gene Summary

Gene:POLK; DNA polymerase kappa
Aliases: DINP, POLQ, DINB1
Location:5q13.3
Summary:This gene encodes a member of the DNA polymerase type-Y family of proteins. The encoded protein is a specialized DNA polymerase that catalyzes translesion DNA synthesis, which allows DNA replication in the presence of DNA lesions. Human cell lines lacking a functional copy of this gene exhibit impaired genome integrity and enhanced susceptibility to oxidative damage. Mutations in this gene that impair enzyme activity may be associated with prostate cancer in human patients. [provided by RefSeq, Sep 2016]
Databases:VEGA, OMIM, HGNC, Ensembl, GeneCard, Gene
Protein:DNA polymerase kappa
Source:NCBIAccessed: 16 March, 2017

Ontology:

What does this gene/protein do?
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Pathways:What pathways are this gene/protein implicaed in?
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Cancer Overview

Research Indicators

Publications Per Year (1992-2017)
Graph generated 16 March 2017 using data from PubMed using criteria.

Literature Analysis

Mouse over the terms for more detail; many indicate links which you can click for dedicated pages about the topic.

Tag cloud generated 16 March, 2017 using data from PubMed, MeSH and CancerIndex

Specific Cancers (6)

Data table showing topics related to specific cancers and associated disorders. Scope includes mutations and abnormal protein expression.

Note: list is not exhaustive. Number of papers are based on searches of PubMed (click on topic title for arbitrary criteria used).

Latest Publications: POLK (cancer-related)

Dai ZJ, Liu XH, Ma YF, et al.
Association Between Single Nucleotide Polymorphisms in DNA Polymerase Kappa Gene and Breast Cancer Risk in Chinese Han Population: A STROBE-Compliant Observational Study.
Medicine (Baltimore). 2016; 95(2):e2466 [PubMed] Free Access to Full Article Related Publications
DNA polymerases are responsible for ensuring stability of the genome and avoiding genotoxicity caused by a variety of factors during DNA replication. Consequently, these proteins have been associated with an increased cancer risk. DNA polymerase kappa (POLK) is a specialized DNA polymerase involved in translesion DNA synthesis (TLS) that allows DNA synthesis over the damaged DNA. Recently, some studies investigated relationships between POLK polymorphisms and cancer risk, but the role of POLK genetic variants in breast cancer (BC) remains to be defined. In this study, we aimed to evaluate the effects of POLK polymorphisms on BC risk.We used the Sequenom MassARRAY method to genotype 3 single nucleotide polymorphisms (SNPs) in POLK (rs3213801, rs10077427, and rs5744533), in order to determine the genotypes of 560 BC patients and 583 controls. The association of genotypes and BC was assessed by computing the odds ratio (OR) and 95% confidence intervals (95% CIs) from logistic regression analyses.We found a statistically significant difference between patient and control groups in the POLK rs10077427 genotypic groups, excluding the recessive model. A positive correlation was also found between positive progesterone receptor (PR) status, higher Ki67 index, and rs10077427 polymorphism. For rs5744533 polymorphism, the codominant, dominant, and allele models frequencies were significantly higher in BC patients compared to healthy controls. Furthermore, our results indicated that rs5744533 SNP has a protective role in the postmenopausal women. However, we failed to find any associations between rs3213801 polymorphism and susceptibility to BC.Our results indicate that POLK polymorphisms may influence the risk of developing BC, and, because of this, may serve as a prognostic biomarker among Chinese women.

Bostian AC, Maddukuri L, Reed MR, et al.
Kynurenine Signaling Increases DNA Polymerase Kappa Expression and Promotes Genomic Instability in Glioblastoma Cells.
Chem Res Toxicol. 2016; 29(1):101-8 [PubMed] Free Access to Full Article Related Publications
Overexpression of the translesion synthesis polymerase hpol κ in glioblastomas has been linked to poor patient prognosis; however, the mechanism promoting higher expression in these tumors remains unknown. We determined that activation of the aryl hydrocarbon receptor (AhR) pathway in glioblastoma cells leads to increased hpol κ mRNA and protein levels. We blocked nuclear translocation and DNA binding by AhR in glioblastoma cells using a small-molecule and observed decreased hpol κ expression. Pharmacological inhibition of tryptophan-2,3-dioxygenase (TDO), the enzyme largely responsible for activating AhR in glioblastoma, led to a decrease in the endogenous AhR agonist kynurenine and a corresponding decrease in hpol κ protein levels. Importantly, we discovered that inhibiting TDO activity, AhR signaling, or suppressing hpol κ expression with RNA interference led to decreased chromosomal damage in glioblastoma cells. Epistasis assays further supported the idea that TDO activity, activation of AhR signaling, and the resulting overexpression of hpol κ function primarily in the same pathway to increase endogenous DNA damage. These findings indicate that upregulation of hpol κ through glioblastoma-specific TDO activity and activation of AhR signaling likely contributes to the high levels of replication stress and genomic instability observed in these tumors.

Edwards L, Gupta R, Filipp FV
Hypermutation of DPYD Deregulates Pyrimidine Metabolism and Promotes Malignant Progression.
Mol Cancer Res. 2016; 14(2):196-206 [PubMed] Free Access to Full Article Related Publications
UNLABELLED: New strategies are needed to diagnose and target human melanoma. To this end, genomic analyses was performed to assess somatic mutations and gene expression signatures using a large cohort of human skin cutaneous melanoma (SKCM) patients from The Cancer Genome Atlas (TCGA) project to identify critical differences between primary and metastatic tumors. Interestingly, pyrimidine metabolism is one of the major pathways to be significantly enriched and deregulated at the transcriptional level in melanoma progression. In addition, dihydropyrimidine dehydrogenase (DPYD) and other important pyrimidine-related genes: DPYS, AK9, CAD, CANT1, ENTPD1, NME6, NT5C1A, POLE, POLQ, POLR3B, PRIM2, REV3L, and UPP2 are significantly enriched in somatic mutations relative to the background mutation rate. Structural analysis of the DPYD protein dimer reveals a potential hotspot of recurring somatic mutations in the ligand-binding sites as well as the interfaces of protein domains that mediated electron transfer. Somatic mutations of DPYD are associated with upregulation of pyrimidine degradation, nucleotide synthesis, and nucleic acid processing while salvage and nucleotide conversion is downregulated in TCGA SKCM.
IMPLICATIONS: At a systems biology level, somatic mutations of DPYD cause a switch in pyrimidine metabolism and promote gene expression of pyrimidine enzymes toward malignant progression.

Gee HE, Buffa FM, Harris AL, et al.
MicroRNA-Related DNA Repair/Cell-Cycle Genes Independently Associated With Relapse After Radiation Therapy for Early Breast Cancer.
Int J Radiat Oncol Biol Phys. 2015; 93(5):1104-14 [PubMed] Related Publications
PURPOSE: Local recurrence and distant failure after adjuvant radiation therapy for breast cancer remain significant clinical problems, incompletely predicted by conventional clinicopathologic markers. We had previously identified microRNA-139-5p and microRNA-1274a as key regulators of breast cancer radiation response in vitro. The purpose of this study was to investigate standard clinicopathologic markers of local recurrence in a contemporary series and to establish whether putative target genes of microRNAs involved in DNA repair and cell cycle control could better predict radiation therapy response in vivo.
METHODS AND MATERIALS: With institutional ethics board approval, local recurrence was measured in a contemporary, prospectively collected series of 458 patients treated with radiation therapy after breast-conserving surgery. Additionally, independent publicly available mRNA/microRNA microarray expression datasets totaling >1000 early-stage breast cancer patients, treated with adjuvant radiation therapy, with >10 years of follow-up, were analyzed. The expression of putative microRNA target biomarkers--TOP2A, POLQ, RAD54L, SKP2, PLK2, and RAG1--were correlated with standard clinicopathologic variables using 2-sided nonparametric tests, and to local/distant relapse and survival using Kaplan-Meier and Cox regression analysis.
RESULTS: We found a low rate of isolated local recurrence (1.95%) in our modern series, and that few clinicopathologic variables (such as lymphovascular invasion) were significantly predictive. In multiple independent datasets (n>1000), however, high expression of RAD54L, TOP2A, POLQ, and SKP2 significantly correlated with local recurrence, survival, or both in univariate and multivariate analyses (P<.001). Low RAG1 expression significantly correlated with local recurrence (multivariate, P=.008). Additionally, RAD54L, SKP2, and PLK2 may be predictive, being prognostic in radiation therapy-treated patients but not in untreated matched control individuals (n=107; P<.05).
CONCLUSIONS: Biomarkers of DNA repair and cell cycle control can identify patients at high risk of treatment failure in those receiving radiation therapy for early breast cancer in independent cohorts. These should be further investigated prospectively, especially TOP2A and SKP2, for which targeted therapies are available.

Cheng PH, Rao XM, Wechman SL, et al.
Oncolytic adenovirus targeting cyclin E overexpression repressed tumor growth in syngeneic immunocompetent mice.
BMC Cancer. 2015; 15:716 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Clinical trials have indicated that preclinical results obtained with human tumor xenografts in mouse models may overstate the potential of adenovirus (Ad)-mediated oncolytic therapies. We have previously demonstrated that the replication of human Ads depends on cyclin E dysregulation or overexpression in cancer cells. ED-1 cell derived from mouse lung adenocarcinomas triggered by transgenic overexpression of human cyclin E may be applied to investigate the antitumor efficacy of oncolytic Ads.
METHODS: Ad-cycE was used to target cyclin E overexpression in ED-1 cells and repress tumor growth in a syngeneic mouse model for investigation of oncolytic virotherapies.
RESULTS: Murine ED-1 cells were permissive for human Ad replication and Ad-cycE repressed ED-1 tumor growth in immunocompetent FVB mice. ED-1 cells destroyed by oncolytic Ads in tumors were encircled in capsule-like structures, while cells outside the capsules were not infected and survived the treatment.
CONCLUSION: Ad-cycE can target cyclin E overexpression in cancer cells and repress tumor growth in syngeneic mouse models. The capsule structures formed after Ad intratumoral injection may prevent viral particles from spreading to the entire tumor.

Abegglen LM, Caulin AF, Chan A, et al.
Potential Mechanisms for Cancer Resistance in Elephants and Comparative Cellular Response to DNA Damage in Humans.
JAMA. 2015; 314(17):1850-60 [PubMed] Free Access to Full Article Related Publications
IMPORTANCE: Evolutionary medicine may provide insights into human physiology and pathophysiology, including tumor biology.
OBJECTIVE: To identify mechanisms for cancer resistance in elephants and compare cellular response to DNA damage among elephants, healthy human controls, and cancer-prone patients with Li-Fraumeni syndrome (LFS).
DESIGN, SETTING, AND PARTICIPANTS: A comprehensive survey of necropsy data was performed across 36 mammalian species to validate cancer resistance in large and long-lived organisms, including elephants (n = 644). The African and Asian elephant genomes were analyzed for potential mechanisms of cancer resistance. Peripheral blood lymphocytes from elephants, healthy human controls, and patients with LFS were tested in vitro in the laboratory for DNA damage response. The study included African and Asian elephants (n = 8), patients with LFS (n = 10), and age-matched human controls (n = 11). Human samples were collected at the University of Utah between June 2014 and July 2015.
EXPOSURES: Ionizing radiation and doxorubicin.
MAIN OUTCOMES AND MEASURES: Cancer mortality across species was calculated and compared by body size and life span. The elephant genome was investigated for alterations in cancer-related genes. DNA repair and apoptosis were compared in elephant vs human peripheral blood lymphocytes.
RESULTS: Across mammals, cancer mortality did not increase with body size and/or maximum life span (eg, for rock hyrax, 1% [95% CI, 0%-5%]; African wild dog, 8% [95% CI, 0%-16%]; lion, 2% [95% CI, 0%-7%]). Despite their large body size and long life span, elephants remain cancer resistant, with an estimated cancer mortality of 4.81% (95% CI, 3.14%-6.49%), compared with humans, who have 11% to 25% cancer mortality. While humans have 1 copy (2 alleles) of TP53, African elephants have at least 20 copies (40 alleles), including 19 retrogenes (38 alleles) with evidence of transcriptional activity measured by reverse transcription polymerase chain reaction. In response to DNA damage, elephant lymphocytes underwent p53-mediated apoptosis at higher rates than human lymphocytes proportional to TP53 status (ionizing radiation exposure: patients with LFS, 2.71% [95% CI, 1.93%-3.48%] vs human controls, 7.17% [95% CI, 5.91%-8.44%] vs elephants, 14.64% [95% CI, 10.91%-18.37%]; P < .001; doxorubicin exposure: human controls, 8.10% [95% CI, 6.55%-9.66%] vs elephants, 24.77% [95% CI, 23.0%-26.53%]; P < .001).
CONCLUSIONS AND RELEVANCE: Compared with other mammalian species, elephants appeared to have a lower-than-expected rate of cancer, potentially related to multiple copies of TP53. Compared with human cells, elephant cells demonstrated increased apoptotic response following DNA damage. These findings, if replicated, could represent an evolutionary-based approach for understanding mechanisms related to cancer suppression.

Rice J, Roberts H, Rai SN, Galandiuk S
Housekeeping genes for studies of plasma microRNA: A need for more precise standardization.
Surgery. 2015; 158(5):1345-51 [PubMed] Related Publications
INTRODUCTION: Plasma microRNAs (miRNAs) are promising biomarkers for many forms of cancer in humans; however, a fundamental concern is the lack of standardization in current data acquisition and reporting. Part of this problem lies in the use of numerous, different housekeeping genes (HKG) for the acquisition of real-time polymerase chain reaction data. This existing practice of using different HKGs generally is accepted, but reproducibility of data for comparison and validation between different laboratories calls for improvement. The need for data reproducibility standardization is crucial. An ideal plasma HKG (1) should be expressed in all samples, (2) have medium-to-high levels of expression, and (3) have consistently measurable levels of expression.
METHODS: Total RNA was extracted from 200-μL plasma samples via a modified miRNeasy (QIAGEN) extraction technique with yeast carrier. Total RNA purity was assessed with a Nanodrop 2000 spectrophotometer (Thermo Scientific). The cycle threshold (Ct) was fixed at 0.03 for all samples. We investigated 10 potential HKGs based both on reports in the literature and our previous data. The potential HKGs were Let-7a, Let-7d, Let-7g, miR-16, RNU6, RNU48, miR-191, miR-223, miR-484, and miR-520d-5p. Once all samples were run for each potential HKG, the mean Ct and SD was calculated for all sample groups, allowing for comparison among HKGs.
RESULTS: We screened 380 miRNAs by using microfluidic array technology (Applied Biosystems) in a discovery cohort of 20 colorectal cancer (CRC) patients, 10 patients each with breast cancer (BC), lung cancer (LC), pancreatic cancer (PC), 11 patients with colorectal adenoma, and 12 controls. The mean Ct and SD was calculated for RNU6, miR-520d-5p, miR-16, miR-191, miR-223, and miR-484, which were expressed in all samples. Let-7a, Let-7d, Let-7g, and RNU48 were only expressed in 26%, 7%, 10%, and 8% of samples, respectively, and therefore were deemed to be insufficiently reliable HKGs. Only miRNAs with >50% expression were included in this statistical analysis. U6 and miR-520d-5p had the most consistent Ct as well as the least SD. The use of both RNU6 and 520d-5p as HKGs provided reliable results.
CONCLUSION: Among HKGs that were expressed in all samples, we suggest that RNU6 and miR-520d-5p were the best candidates for HKGs for studies of plasma miRNA because of the consistent and high Ct in all samples and a very narrow, reproducible SD.

Yadav S, Mukhopadhyay S, Anbalagan M, Makridakis N
Somatic Mutations in Catalytic Core of POLK Reported in Prostate Cancer Alter Translesion DNA Synthesis.
Hum Mutat. 2015; 36(9):873-80 [PubMed] Free Access to Full Article Related Publications
DNA polymerase kappa is a Y-family polymerase that participates to bypass the damaged DNA known as translesion synthesis (TLS) polymerase. Higher frequency of mutations in DNA polymerase kappa (POLK) recently been reported in prostate cancer. We sequenced entire exons of the POLK gene on genomic DNA from 40 prostate cancers and matched normal samples. We identified that 28% of patients have somatic mutations in the POLK gene of the prostate tumors. Mutations in these prostate cancers have somatic mutation spectra, which are dominated by C-to-T transitions. In the current study, we further investigate the effect of p.E29K, p.G154E, p.F155S, p.E430K, p.L442F, and p.E449K mutations on the biochemical properties of the polymerase in vitro, using TLS assay and nucleotide incorporation fidelity, following site-directed mutagenesis bacterial expression, and purification of the respective polymerase variants. We report that following missense mutations p.E29K, p.G154E, p.F155S, p.E430K, and p.L442F significantly diminished the catalytic efficiencies of POLK with regard to the lesion bypass (AP site). POLK variants show extraordinarily low fidelity by misincorporating T, C, and G as compared to wild-type variants. Taken together, these results suggest that interfering with normal polymerase kappa function by these mutations may be involved in prostate carcinogenesis.

Hong SH, Tilan JU, Galli S, et al.
High neuropeptide Y release associates with Ewing sarcoma bone dissemination - in vivo model of site-specific metastases.
Oncotarget. 2015; 6(9):7151-65 [PubMed] Free Access to Full Article Related Publications
Ewing sarcoma (ES) develops in bones or soft tissues of children and adolescents. The presence of bone metastases is one of the most adverse prognostic factors, yet the mechanisms governing their formation remain unclear. As a transcriptional target of EWS-FLI1, the fusion protein driving ES transformation, neuropeptide Y (NPY) is highly expressed and released from ES tumors. Hypoxia up-regulates NPY and activates its pro-metastatic functions. To test the impact of NPY on ES metastatic pattern, ES cell lines, SK-ES1 and TC71, with high and low peptide release, respectively, were used in an orthotopic xenograft model. ES cells were injected into gastrocnemius muscles of SCID/beige mice, the primary tumors excised, and mice monitored for the presence of metastases. SK-ES1 xenografts resulted in thoracic extra-osseous metastases (67%) and dissemination to bone (50%) and brain (25%), while TC71 tumors metastasized to the lungs (70%). Bone dissemination in SK-ES1 xenografts associated with increased NPY expression in bone metastases and its accumulation in bone invasion areas. The genetic silencing of NPY in SK-ES1 cells reduced bone degradation. Our study supports the role for NPY in ES bone invasion and provides new models for identifying pathways driving ES metastases to specific niches and testing anti-metastatic therapeutics.

Ceccaldi R, Liu JC, Amunugama R, et al.
Homologous-recombination-deficient tumours are dependent on Polθ-mediated repair.
Nature. 2015; 518(7538):258-62 [PubMed] Free Access to Full Article Related Publications
Large-scale genomic studies have shown that half of epithelial ovarian cancers (EOCs) have alterations in genes regulating homologous recombination (HR) repair. Loss of HR accounts for the genomic instability of EOCs and for their cellular hyper-dependence on alternative poly-ADP ribose polymerase (PARP)-mediated DNA repair mechanisms. Previous studies have implicated the DNA polymerase θ (Polθ also known as POLQ, encoded by POLQ) in a pathway required for the repair of DNA double-strand breaks, referred to as the error-prone microhomology-mediated end-joining (MMEJ) pathway. Whether Polθ interacts with canonical DNA repair pathways to prevent genomic instability remains unknown. Here we report an inverse correlation between HR activity and Polθ expression in EOCs. Knockdown of Polθ in HR-proficient cells upregulates HR activity and RAD51 nucleofilament assembly, while knockdown of Polθ in HR-deficient EOCs enhances cell death. Consistent with these results, genetic inactivation of an HR gene (Fancd2) and Polq in mice results in embryonic lethality. Moreover, Polθ contains RAD51 binding motifs and it blocks RAD51-mediated recombination. Our results reveal a synthetic lethal relationship between the HR pathway and Polθ-mediated repair in EOCs, and identify Polθ as a novel druggable target for cancer therapy.

Family L, Bensen JT, Troester MA, et al.
Single-nucleotide polymorphisms in DNA bypass polymerase genes and association with breast cancer and breast cancer subtypes among African Americans and Whites.
Breast Cancer Res Treat. 2015; 149(1):181-90 [PubMed] Free Access to Full Article Related Publications
DNA damage recognition and repair is a complex system of genes focused on maintaining genomic stability. Recently, there has been a focus on how breast cancer susceptibility relates to genetic variation in the DNA bypass polymerases pathway. Race-stratified and subtype-specific logistic regression models were used to estimate odds ratios (ORs) and 95 % confidence intervals (CIs) for the association between 22 single-nucleotide polymorphisms (SNPs) in seven bypass polymerase genes and breast cancer risk in the Carolina Breast Cancer Study, a population-based, case-control study (1,972 cases and 1,776 controls). We used SNP-set kernel association test (SKAT) to evaluate the multi-gene, multi-locus (combined) SNP effects within bypass polymerase genes. We found similar ORs for breast cancer with three POLQ SNPs (rs487848 AG/AA vs. GG; OR = 1.31, 95 % CI 1.03-1.68 for Whites and OR = 1.22, 95 % CI 1.00-1.49 for African Americans), (rs532411 CT/TT vs. CC; OR = 1.31, 95 % CI 1.02-1.66 for Whites and OR = 1.22, 95 % CI 1.00-1.48 for African Americans), and (rs3218634 CG/CC vs. GG; OR = 1.29, 95 % CI 1.02-1.65 for Whites). These three SNPs are in high linkage disequilibrium in both races. Tumor subtype analysis showed the same SNPs to be associated with increased risk of Luminal breast cancer. SKAT analysis showed no significant combined SNP effects. These results suggest that variants in the POLQ gene may be associated with the risk of Luminal breast cancer.

Brandalize AP, Schüler-Faccini L, Hoffmann JS, et al.
A DNA repair variant in POLQ (c.-1060A > G) is associated to hereditary breast cancer patients: a case-control study.
BMC Cancer. 2014; 14:850 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: One of the hallmarks of cancer is the occurrence of high levels of chromosomal rearrangements as a result of inaccurate repair of double-strand breaks (DSB). Germline mutations in BRCA and RAD51 genes, involved in DSB repair, are strongly associated with hereditary breast cancer. Pol θ, a translesional DNA polymerase specialized in the replication of damaged DNA, has been also shown to contribute to DNA synthesis associated to DSB repair. It is noteworthy that POLQ is highly expressed in breast tumors and this expression is able to predict patient outcome. The objective of this study was to analyze genetic variants related to POLQ as new population biomarkers of risk in hereditary (HBC) and sporadic (SBC) breast cancer.
METHODS: We analyzed through case-control study nine SNPs of POLQ in hereditary (HBC) and sporadic (SBC) breast cancer patients using Taqman Real Time PCR assays. Polymorphisms were systematically identified through the NCBI database and are located within exons or promoter regions. We recruited 204 breast cancer patients (101 SBC and 103 HBC) and 212 unaffected controls residing in Southern Brazil.
RESULTS: The rs581553 SNP located in the promoter region was strongly associated with HBC (c.-1060A > G; HBC GG = 15, Control TT = 8; OR = 5.67, CI95% = 2.26-14.20; p < 0.0001). Interestingly, 11 of 15 homozygotes for this polymorphism fulfilled criteria for Hereditary Breast and Ovarian Cancer (HBOC) syndrome. Furthermore, 12 of them developed bilateral breast cancer and one had a familial history of bilateral breast cancer. This polymorphism was also associated with bilateral breast cancer in 67 patients (OR = 9.86, CI95% = 3.81-25.54). There was no statistically significant difference of age at breast cancer diagnosis between SNP carriers and non-carriers.
CONCLUSIONS: Considering that Pol θ is involved in DBS repair, our results suggest that this polymorphism may contribute to the etiology of HBC, particularly in patients with bilateral breast cancer.

Egger ME, McNally LR, Nitz J, et al.
Adenovirus-mediated FKHRL1/TM sensitizes melanoma cells to apoptosis induced by temozolomide.
Hum Gene Ther Clin Dev. 2014; 25(3):186-95 [PubMed] Free Access to Full Article Related Publications
Melanoma exhibits variable resistance to the alkylating agent temozolomide (TMZ). We evaluated the potential of adenovirus expressing forkhead human transcription factor like 1 triple mutant (Ad-FKHRL1/TM) to sensitize melanoma cells to TMZ. Four melanoma cell lines were treated with Ad-FKHRL1/TM and TMZ, alone or in combination. Apoptosis was assessed by activation and inhibition of caspase pathway, nuclei fragmentation, and annexin V staining. The potential therapeutic efficacy of Ad-FKHRL1/TM with TMZ was also assessed in a mouse melanoma xenograft model. Combination therapy of Ad-FKHRL1/TM and TMZ resulted in greater cell killing (<20% cell viability) compared with single therapy and controls (p<0.05). Combination indices of Ad-FKHRL1/TM and TMZ therapy indicated significant (p<0.05) synergistic killing effect. Greater apoptosis induction was found in cells treated with Ad-FKHRL1/TM and TMZ than with Ad-FKHRL1/TM or TMZ-treated cells alone. Treatment with TMZ enhanced adenovirus transgene expression in a cell type-dependent manner. In an in vivo model, combination therapy of Ad-FKHRL1/TM with TMZ results in greater tumor growth reduction in comparison with single treatments. We suggest that Ad-FKHRL1/TM is a promising vector to sensitize melanoma cells to TMZ, and that a combination of both approaches would be effective in the clinical setting.

Yang S, Zhang H, Guo L, et al.
Reconstructing the coding and non-coding RNA regulatory networks of miRNAs and mRNAs in breast cancer.
Gene. 2014; 548(1):6-13 [PubMed] Related Publications
microRNAs (miRNAs) are a class of small non-coding RNAs that deregulate and/or decrease the expression of target messenger RNAs (mRNAs), which specifically contribute to complex diseases. In our study, we reanalyzed an integrated data to promote classification performance by rebuilding miRNA-mRNA modules, in which a group of deregulated miRNAs cooperatively regulated a group of significant mRNAs. In five-fold cross validation, the multiple processes flow considered the biological and statistical significant correlations. First, of statistical significant miRNAs, 6 were identified as core miRNAs. Second, in the 13 significant pathways enriched by gene set enrichment analysis (GSEA), 705 deregulated mRNAs were found. Based on the union of predicted sets and correlation sets, 6 modules were built. Finally, after verified by test sets, three indexes, including area under the ROC curve (AUC), Accuracy and Matthews correlation coefficients (MCCs), indicated only 4 modules (miR-106b-CIT-KPNA2-miR-93, miR-106b-POLQ-miR-93, miR-107-BTRC-UBR3-miR-16 and miR-200c-miR-16-EIF2B5-miR-15b) had discriminated ability and their classification performance were prior to that of the single molecules. By applying this flow to different subtypes, Module 1 was the consistent module across subtypes, but some different modules were still specific to each subtype. Taken together, this method gives new insight to building modules related to complex diseases and simultaneously can give a supplement to explain the mechanism of breast cancer (BC).

Shao M, Jin B, Niu Y, et al.
Association of POLK polymorphisms with platinum-based chemotherapy response and severe toxicity in non-small cell lung cancer patients.
Cell Biochem Biophys. 2014; 70(2):1227-37 [PubMed] Related Publications
Lung cancer is the leading cause of tumor-derived death. Although target therapy is proven very efficient, traditionally platinum-based chemotherapies are still primary treatment for most patients. Platinum can suppress the tumor growth and impair normal cells together. The primary aim of the present study was to study the potential role of translesion synthesis (TLS) that might play in platinum-chemotherapy tolerance and side-effect. In present study, a total of 663 patients who were newly histologically diagnosed with advanced NSCLC (aNSCLC) were enrolled. Treatment response was classified into four categories: complete response, partial response, stable disease, and progressive disease. Incidence of gastrointestinal and hematological toxicities was assessed twice a week during the whole first-line treatment. Eleven SNPs of POLK were genotyped. The associations between SNPs and treatment response or toxicity were analyzed with logistic regression model. Cox regression was used for survival analysis between SNPs and progression-free survival or overall survival. We identified that rs3213801 and rs5744533 showed complete linkage in the present study, and they were significantly associated with treatment response (adjusted P = 0.044), together with rs5744655 (adjusted P = 0.039). rs1018119 was correlated with gastrointestinal toxicity in smokers specially (adjusted P = 0.041). Besides, rs3756558 was associated with hematological toxicity and overall toxicity in smokers and combined cohort with additive model. We also identified the significant association between two SNPs, rs10077427 and rs5744545, and PFS. The polymorphism of POLK, an important gene in TLS, participates in platinum-chemotherapy tolerance and side-effect.

Wang T, Feldman AL, Wada DA, et al.
GATA-3 expression identifies a high-risk subset of PTCL, NOS with distinct molecular and clinical features.
Blood. 2014; 123(19):3007-15 [PubMed] Free Access to Full Article Related Publications
The cell of origin and the tumor microenvironment's role remain elusive for the most common peripheral T-cell lymphomas (PTCLs). As macrophages promote the growth and survival of malignant T cells and are abundant constituents of the tumor microenvironment, their functional polarization was examined in T-cell lymphoproliferative disorders. Cytokines that are abundant within the tumor microenvironment, particularly interleukin (IL)-10, were observed to promote alternative macrophage polarization. Macrophage polarization was signal transducer and activator of transcription 3 dependent and was impaired by the Janus kinase inhibitor ruxolitinib. In conventional T cells, the production of T helper (Th)2-associated cytokines and IL-10, both of which promote alternative macrophage polarization, is regulated by the T-cell transcription factor GATA-binding protein 3 (GATA-3). Therefore, its role in the T-cell lymphomas was examined. GATA-3 expression was observed in 45% of PTCLs, not otherwise specified (PTCL, NOS) and was associated with distinct molecular features, including the production of Th2-associated cytokines. In addition, GATA-3 expression identified a subset of PTCL, NOS with distinct clinical features, including inferior progression-free and overall survival. Collectively, these data suggest that further understanding the cell of origin and lymphocyte ontogeny among the T-cell lymphomas may improve our understanding of the tumor microenvironment's pathogenic role in these aggressive lymphomas.

Santarpia L, Iwamoto T, Di Leo A, et al.
DNA repair gene patterns as prognostic and predictive factors in molecular breast cancer subtypes.
Oncologist. 2013; 18(10):1063-73 [PubMed] Free Access to Full Article Related Publications
DNA repair pathways can enable tumor cells to survive DNA damage induced by chemotherapy and thus provide prognostic and/or predictive value. We evaluated Affymetrix gene expression profiles for 145 DNA repair genes in untreated breast cancer (BC) patients (n = 684) and BC patients treated with regimens containing neoadjuvant taxane/anthracycline (n = 294) or anthracycline (n = 210). We independently assessed estrogen receptor (ER)-positive/HER2-negative, HER2-positive, and ER-negative/HER2-negative subgroups for differential expression, bimodal distribution, and the prognostic and predictive value of DNA repair gene expression. Twenty-two genes were consistently overexpressed in ER-negative tumors, and five genes were overexpressed in ER-positive tumors, but no differences in expression were associated with HER2 status. In ER-positive/HER2-negative tumors, the expression of nine genes (BUB1, FANCI, MNAT1, PARP2, PCNA, POLQ, RPA3, TOP2A, and UBE2V2) was associated with poor prognosis, and the expression of one gene (ATM) was associated with good prognosis. Furthermore, the prognostic value of specific genes did not correlate with proliferation. A few genes were associated with chemotherapy response in BC subtypes and treatment-specific manner. In ER-negative/HER2-negative tumors, the MSH2, MSH6, and FAN1 (previously MTMR15) genes were associated with pathological complete response and residual invasive cancer in taxane/anthracycline-treated patients. Conversely, PMS2 expression was associated with residual invasive cancer in treatments using anthracycline as a single agent. In HER2-positive tumors, TOP2A was associated with patient response to anthracyclines but not to taxane/anthracycline regimens. In genes expressed in a bimodal fashion, RECQL4 was significantly associated with clinical outcome. In vitro studies showed that defects in RECQL4 impair homologous recombination, sensitizing BC cells to DNA-damaging agents.

Kanaan Z, Roberts H, Eichenberger MR, et al.
A plasma microRNA panel for detection of colorectal adenomas: a step toward more precise screening for colorectal cancer.
Ann Surg. 2013; 258(3):400-8 [PubMed] Related Publications
OBJECTIVE: The main objective of this study was to investigate the potential use of circulating microRNAs (miRNAs) as biomarkers of colorectal (CR) adenomas.
BACKGROUND: Detection of precancerous lesions such as CR adenoma is a key to reduce CR cancer (CRC) mortality. There is a great need for accurate, noninvasive biomarkers for detection of CR adenoma and CRC. MiRNAs are non-protein-coding RNAs that regulate gene expression. Our prior work investigated the dysregulation of 5 plasma miRNAs in CRC patients. As intended, we undertook a more comprehensive plasma-miRNA screening study in patients with CR adenoma and CRC.
METHODS: We screened for 380 plasma-miRNAs using microfluidic array technology (Applied BioSystems) in a screening cohort of 12 healthy controls, 9 patients with CR adenomas, and 20 patients with CRC. A panel of the most dysregulated miRNAs (P < 0.05, False Discovery Rate: 5%) was then validated in a blinded cohort of 26 healthy controls, 16 patients with large adenomas, and 45 patients with CRC.
RESULTS: A panel of 8 plasma miRNAs (miR-532-3p, miR-331, miR-195, miR-17, miR-142-3p, miR-15b, miR-532, and miR-652) distinguished polyps from controls with high accuracy [area under curve (AUC) = 0.868 (95% confidence interval [CI]: 0.76-0.98)]. In addition, a panel of 3 plasma miRNAs (miR-431, miR-15b, and miR-139-3p) distinguished Stage IV CRC from controls with an [AUC = 0.896 (95% CI: 0.78-1.0)]. Receiver-operating-characteristic curves of miRNA panels for all CRC versus controls and polyps versus all CRC showed AUC values of 0.829 (95% CI: 0.73-0.93) and 0.856 (95% CI: 0.75-0.97), respectively.
CONCLUSIONS: Plasma miRNAs are reliable, noninvasive, and inexpensive markers for CR adenomas. This miRNA panel warrants study in larger cohorts. Plasma-based assays could provide better screening compliance compared to fecal occult blood or endoscopic screening.

Li WQ, Hu N, Hyland PL, et al.
Genetic variants in DNA repair pathway genes and risk of esophageal squamous cell carcinoma and gastric adenocarcinoma in a Chinese population.
Carcinogenesis. 2013; 34(7):1536-42 [PubMed] Free Access to Full Article Related Publications
The DNA repair pathways help to maintain genomic integrity and therefore genetic variation in the pathways could affect the propensity to develop cancer. Selected germline single nucleotide polymorphisms (SNPs) in the pathways have been associated with esophageal cancer and gastric cancer (GC) but few studies have comprehensively examined the pathway genes. We aimed to investigate associations between DNA repair pathway genes and risk of esophageal squamous cell carcinoma (ESCC) and GC, using data from a genome-wide association study in a Han Chinese population where ESCC and GC are the predominant cancers. In sum, 1942 ESCC cases, 1758 GC cases and 2111 controls from the Shanxi Upper Gastrointestinal Cancer Genetics Project (discovery set) and the Linxian Nutrition Intervention Trials (replication set) were genotyped for 1675 SNPs in 170 DNA repair-related genes. Logistic regression models were applied to evaluate SNP-level associations. Gene- and pathway-level associations were determined using the resampling-based adaptive rank-truncated product approach. The DNA repair pathways overall were significantly associated with risk of ESCC (P = 6.37 × 10(-4)), but not with GC (P = 0.20). The most significant gene in ESCC was CHEK2 (P = 2.00 × 10(-6)) and in GC was CLK2 (P = 3.02 × 10(-4)). We observed several other genes significantly associated with either ESCC (SMUG1, TDG, TP53, GTF2H3, FEN1, POLQ, HEL308, RAD54B, MPG, FANCE and BRCA1) or GC risk (MRE11A, RAD54L and POLE) (P < 0.05). We provide evidence for an association between specific genes in the DNA repair pathways and the risk of ESCC and GC. Further studies are warranted to validate these associations and to investigate underlying mechanisms.

Yousefzadeh MJ, Wood RD
DNA polymerase POLQ and cellular defense against DNA damage.
DNA Repair (Amst). 2013; 12(1):1-9 [PubMed] Free Access to Full Article Related Publications
In mammalian cells, POLQ (pol θ) is an unusual specialized DNA polymerase whose in vivo function is under active investigation. POLQ has been implicated by different experiments to play a role in resistance to ionizing radiation and defense against genomic instability, in base excision repair, and in immunological diversification. The protein is formed by an N-terminal helicase-like domain, a C-terminal DNA polymerase domain, and a large central domain that spans between the two. This arrangement is also found in the Drosophila Mus308 protein, which functions in resistance to DNA interstrand crosslinking agents. Homologs of POLQ and Mus308 are found in multicellular eukaryotes, including plants, but a comparison of phenotypes suggests that not all of these genes are functional orthologs. Flies defective in Mus308 are sensitive to DNA interstrand crosslinking agents, while mammalian cells defective in POLQ are primarily sensitive to DNA double-strand breaking agents. Cells from Polq(-/-) mice are hypersensitive to radiation and peripheral blood cells display increased spontaneous and ionizing radiation-induced levels of micronuclei (a hallmark of gross chromosomal aberrations), though mice apparently develop normally. Loss of POLQ in human and mouse cells causes sensitivity to ionizing radiation and other double strand breaking agents and increased DNA damage signaling. Retrospective studies of clinical samples show that higher levels of POLQ gene expression in breast and colorectal cancer are correlated with poorer outcomes for patients. A clear understanding of the mechanism of action and physiologic function of POLQ in the cell is likely to bear clinical relevance.

Billeter AT, Barnett RE, Druen D, et al.
MicroRNA as a new factor in lung and esophageal cancer.
Semin Thorac Cardiovasc Surg. 2012; 24(3):155-65 [PubMed] Related Publications
Lung cancer is the most lethal cancer due to late detection in advanced stages; early diagnosis of lung cancer allows surgical treatment and improves the outcome. The prevalence of gastroesophageal reflux-related adenocarcinomas of the esophagus is increasing; repetitive surveillance endoscopies are necessary to detect development of cancer. A blood-based biomarker would simplify the diagnosis and treatment of both diseases. MicroRNAs (miRNAs) are short RNA strands that interfere with protein production. miRNAs play pivotal roles in cell homeostasis, and dysregulation of miRNAs can lead to the development of cancer. miRNAs can be found in all body fluids and have been proposed to serve as messengers between closely localized cells but also distant organs. Cancer cells actively secrete miRNAs, and these miRNA profiles can be found in blood. We outline, here, how these miRNAs may aid in diagnosis and treatment of lung and esophageal cancers, as well as their apparent limitations.

Lessa RC, Campos AH, Freitas CE, et al.
Identification of upregulated genes in oral squamous cell carcinomas.
Head Neck. 2013; 35(10):1475-81 [PubMed] Related Publications
BACKGROUND: Oral cancer is the most common subset of head and neck squamous cell carcinomas (HNSCC). These tumors often have an aggressive clinical outcome hallmarked by a propensity for local invasion and regional nodal metastasis. Upregulated genes could be useful as markers for diagnosis, prognosis, and as new drug targets for these tumors.
METHODS: To identify upregulated genes in oral squamous cell carcinomas (OSSCs), we examined the ORESTES public database and used a quantitative reverse transcription-polymerase chain reaction (qRT-PCR) approach to determine the expression level of selected genes in tumor samples.
RESULTS AND CONCLUSIONS: The ORESTES data mining analysis indicated 40 upregulated genes in HNSCC. Nine of these candidate genes were selected for further qRT-PCR validation and 3 of them (ALDOA, AHSA1, and POLQ) were frequently found upregulated in OSCC samples, which may indicate an association of these genes with the carcinogenesis process in this tumor site and they can constitute potential new targets for therapy.

Kanaan Z, Rai SN, Eichenberger MR, et al.
Plasma miR-21: a potential diagnostic marker of colorectal cancer.
Ann Surg. 2012; 256(3):544-51 [PubMed] Related Publications
OBJECTIVES: The main objective of this study was to investigate the potential use of circulating microRNAs (miRNAs) as biomarkers of sporadic colorectal cancer (CRC).
BACKGROUND: CRC, a leading cause of death, is curable if detected early. There is an unmet need for an accurate, noninvasive biomarker of CRC. MiRNAs are non-protein-coding RNAs regulating gene expression that play a role in CRC development.
METHODS: Levels of 380 miRNAs were determined using microfluidic array technology (Applied Biosystems) in a "training" set of 30 CRC patients from whom cancer and adjacent normal tissue were collected. The 4 most dysregulated miRNAs (P < 0.05, false discovery rate (FDR): 10%) were then validated in a second blinded "test" set of 16 CRC patients from whom cancer and normal adjacent tissue had been collected. Validated tissue miRNAs were then evaluated in a plasma "test" set consisting of 30 CRC patients and 30 individuals without CRC. The most dysregulated tissue miRNAs were then validated in an independent new plasma test set consisting of 20 CRC patients with 20 age-, -, and race-matched subjects without CRC.
RESULTS: Nineteen of 380 miRNAs were dysregulated in CRC tissue in the tissue "training" set (P < 0.05, FDR: 10%). The 2 most upregulated (miR-31; miR-135b) and most downregulated (miR-1; miR-133a) miRNAs identified CRC in our "test" set with 100% sensitivity and 80% specificity. MiR-31 was more upregulated in stages III and IV compared with stages I and II (P < 0.05). In the "plasma" group, miR-21 differentiated CRC patients from controls with 90% specificity and sensitivity.
CONCLUSIONS: Plasma miRNAs provide reliable and noninvasive markers for CRC. Plasma miR-21 warrants study in larger cohorts. It seems uniquely promising as a plasma biomarker for CRC.

Dubé PE, Yan F, Punit S, et al.
Epidermal growth factor receptor inhibits colitis-associated cancer in mice.
J Clin Invest. 2012; 122(8):2780-92 [PubMed] Free Access to Full Article Related Publications
Inflammatory bowel disease (IBD) is a chronic illness caused by complex interactions between genetic and environmental factors that propagate inflammation and damage to the gastrointestinal epithelium. This state of chronic inflammation increases the risk for development of colitis-associated cancer in IBD patients. Thus, the development of targeted therapeutics that can disrupt the cycle of inflammation and epithelial injury is highly attractive. However, such biological therapies, including those targeting epidermal growth factor receptor pathways, pose a risk of increasing cancer rates. Using two mouse models of colitis-associated cancer, we found that epidermal growth factor receptor inactivation accelerated the incidence and progression of colorectal tumors. By modulating inflammation and epithelial regeneration, epidermal growth factor receptor optimized the response to chronic inflammation and limited subsequent tumorigenesis. These findings provide important insights into the pathogenesis of colitis-associated cancer and suggest that epidermal growth factor-based therapies for IBD may reduce long-term cancer risk.

Chaturvedi R, Asim M, Romero-Gallo J, et al.
Spermine oxidase mediates the gastric cancer risk associated with Helicobacter pylori CagA.
Gastroenterology. 2011; 141(5):1696-708.e1-2 [PubMed] Free Access to Full Article Related Publications
BACKGROUND & AIMS: Helicobacter pylori-induced gastric carcinogenesis has been linked to the microbial oncoprotein cytotoxin-associated gene A (CagA). Spermine oxidase (SMO) metabolizes the polyamine spermine into spermidine and generates H(2)O(2), which causes apoptosis and DNA damage. We determined if pathogenic effects of CagA are attributable to SMO.
METHODS: Levels of SMO, apoptosis, and DNA damage (8-oxoguanosine) were measured in gastric epithelial cell lines infected with cagA(+) or cagA(-)H pylori strains, or transfected with a CagA expression plasmid, in the absence or presence of SMO small interfering RNA, or an SMO inhibitor. The role of CagA in induction of SMO and DNA damage was assessed in H pylori-infected gastritis tissues from humans, gerbils, and both wild-type and hypergastrinemic insulin-gastrin mice, using immunohistochemistry and flow cytometry.
RESULTS: cagA(+) strains or ectopic expression of CagA, but not cagA(-) strains, led to increased levels of SMO, apoptosis, and DNA damage in gastric epithelial cells, and knockdown or inhibition of SMO blocked apoptosis and DNA damage. There was increased SMO expression, apoptosis, and DNA damage in gastric tissues from humans infected with cagA(+), but not cagA(-) strains. In gerbils and mice, DNA damage was CagA-dependent and present in cells that expressed SMO. Gastric epithelial cells with DNA damage that were negative for markers of apoptosis accounted for 42%-69% of cells in gerbils and insulin-gastrin mice with dysplasia and carcinoma.
CONCLUSIONS: By inducing SMO, H pylori CagA generates cells with oxidative DNA damage, and a subpopulation of these cells are resistant to apoptosis and thus at high risk for malignant transformation.

Varadi V, Bevier M, Grzybowska E, et al.
Genetic variation in genes encoding for polymerase ζ subunits associates with breast cancer risk, tumour characteristics and survival.
Breast Cancer Res Treat. 2011; 129(1):235-45 [PubMed] Related Publications
Chromosomal instability is a known hallmark of many cancers. DNA polymerases represent a group of enzymes that are involved in the mechanism of chromosomal instability as they have a central function in DNA metabolism. We hypothesized that genetic variation in the polymerase genes may affect gene expression or protein configuration and by that cancer risk and clinical outcome. We selected four genes encoding for the catalytic subunits of the polymerases β, δ, θ and ζ (POLB, POLD1, POLQ and REV3L, respectively) and two associated proteins (MAD2L2 and REV1) because of their previously reported association with chromosomal instability and/or tumorigenesis. We selected potentially functional and most informative tagging single nucleotide polymorphisms (SNPs) for genotyping in a population-based series of 783 Swedish breast cancer (BC) cases and 1562 controls. SNPs that showed a significant association in the Swedish population were additionally genotyped in a Polish population consisting of 506 familial/early onset BC cases and 568 controls. SNPs in all three polymerase ζ subunit genes associated either with BC risk or prognosis. Two SNPs in REV3L and one SNP in MAD2L2 associated with BC risk: rs462779 (multiplicative model: OR 0.79, 95% CI 0.68-0.92), rs3204953 (dominant model: OR 1.28, 95% CI 1.05-1.56) and rs2233004 (recessive model: OR 0.49, 95% CI 0.28-0.86). Homozygous carriers of the minor allele C of the third SNP in REV3L, rs11153292, had significantly worse survival compared to the TT genotype carriers (HR 2.93, 95% CI 1.34-6.44). Minor allele carriers of two REV1 SNPs (rs6761391 and rs3792142) had significantly more often large tumours and tumours with high histological grade and stage. No association was observed for SNPs in POLB, POLQ and POLD1. Altogether, our data suggest a significant role of genetic variation in the polymerase ζ subunit genes regarding the development and progression of BC.

Higgins GS, Harris AL, Prevo R, et al.
Overexpression of POLQ confers a poor prognosis in early breast cancer patients.
Oncotarget. 2010; 1(3):175-84 [PubMed] Free Access to Full Article Related Publications
Depletion of POLQ (DNA polymerase theta) has recently been shown to render tumour cells more sensitive to radiotherapy whilst having little or no effect on normal tissues. This finding led us to investigate whether tumours that overexpress POLQ are associated with an adverse outcome. We therefore correlated the clinical outcomes of two retrospective series of patients with early breast cancer with the expression levels of POLQ, as determined by microarray gene expression analysis. We found that a significant number of tumours overexpressed POLQ and that overexpression was correlated with ER negative disease (p=0.047) and high tumour grade (p=0.004), both of which are associated with poor clinical outcomes. POLQ overexpression was associated with poor relapse free survival rates on both univariate (HR 5.80; 95% CI, 2.220 to 15.159; p<0.001) and multivariate analysis (HR 8.086; 95% CI 2.340 to 27.948 p=0.001). Analysis of other published clinical series confirmed that POLQ overexpression is associated with adverse clinical outcomes. The poor prognosis associated with POLQ is independent of other clinical or pathological features. The mechanism that causes this adverse outcome remains to be elucidated but may in part arise from resistance to adjuvant treatment. These findings, combined with the limited normal tissue expression of POLQ, make it a very appealing target for possible clinical exploitation.

Lemée F, Bergoglio V, Fernandez-Vidal A, et al.
DNA polymerase theta up-regulation is associated with poor survival in breast cancer, perturbs DNA replication, and promotes genetic instability.
Proc Natl Acad Sci U S A. 2010; 107(30):13390-5 [PubMed] Free Access to Full Article Related Publications
"Replicative stress" is one of the main factors underlying neoplasia from its early stages. Genes involved in DNA synthesis may therefore represent an underexplored source of potential prognostic markers for cancer. To this aim, we generated gene expression profiles from two independent cohorts (France, n=206; United Kingdom, n=117) of patients with previously untreated primary breast cancers. We report here that among the 13 human nuclear DNA polymerase genes, DNA Polymerase (POLQ) is the only one significantly up-regulated in breast cancer compared with normal breast tissues. Importantly, POLQ up-regulation significantly correlates with poor clinical outcome (4.3-fold increased risk of death in patients with high POLQ expression), and this correlation is independent of Cyclin E expression or the number of positive nodes, which are currently considered as markers for poor outcome. POLQ expression provides thus an additional indicator for the survival outcome of patients with high Cyclin E tumor expression or high number of positive lymph nodes. Furthermore, to decipher the molecular consequences of POLQ up-regulation in breast cancer, we generated human MRC5-SV cell lines that stably overexpress POLQ. Strong POLQ expression was directly associated with defective DNA replication fork progression and chromosomal damage. Therefore, POLQ overexpression may be a promising genetic instability and prognostic marker for breast cancer.

Frey MR, Hilliard VC, Mullane MT, Polk DB
ErbB4 promotes cyclooxygenase-2 expression and cell survival in colon epithelial cells.
Lab Invest. 2010; 90(10):1415-24 [PubMed] Free Access to Full Article Related Publications
The ErbB4 receptor tyrosine kinase is expressed at high levels in human and mouse colitis, and inhibits colon epithelial cell apoptosis in the presence of proinflammatory cytokines. In this study, we investigated the molecular mechanisms responsible for ErbB4-induced cell survival. In cultured mouse colon epithelial cells, ErbB4 overexpression resulted in increased levels of cyclooxygenase-2 (COX-2) mRNA and protein; in contrast, ErbB4 knockdown with siRNA blocked COX-2 accumulation in response to tumor necrosis factor. Although ErbB4 is expressed as up to four isoforms in epithelial tissues, its ability to promote COX-2 expression was isoform independent. ErbB4-stimulated COX-2 induction was associated with an increase in mRNA half-life and was blocked by inhibition of Src, phosphatidylinositol (PI) 3-kinase, or epidermal growth factor receptor (EGFR). Furthermore, ErbB4 expression promoted EGFR phosphorylation in the presence of heregulin, implicating ErbB4-EGFR heterodimerization in these responses. As to the cellular responses to ErbB4 activation, increased survival of ErbB4-expressing cells in the presence of proinflammatory cytokines was sensitive to the COX-2 inhibitor celecoxib. Furthermore, ErbB4-overexpressing cells acquired the ability to form colonies in soft agar, indicative of cellular transformation, also in a celecoxib-sensitive manner. Together our data indicate that ErbB4 is a key regulator of COX-2 expression and cellular survival in colon epithelial cells, acting in concert with EGFR through a Src- and PI 3-kinase-dependent mechanism. These results suggest that chronic overexpression of ErbB4 in the context of inflammation could contribute to colitis-associated tumorigenesis by inhibiting colonocyte apoptosis.

Higgins GS, Prevo R, Lee YF, et al.
A small interfering RNA screen of genes involved in DNA repair identifies tumor-specific radiosensitization by POLQ knockdown.
Cancer Res. 2010; 70(7):2984-93 [PubMed] Free Access to Full Article Related Publications
The effectiveness of radiotherapy treatment could be significantly improved if tumor cells could be rendered more sensitive to ionizing radiation (IR) without altering the sensitivity of normal tissues. However, many of the key therapeutically exploitable mechanisms that determine intrinsic tumor radiosensitivity are largely unknown. We have conducted a small interfering RNA (siRNA) screen of 200 genes involved in DNA damage repair aimed at identifying genes whose knockdown increased tumor radiosensitivity. Parallel siRNA screens were conducted in irradiated and unirradiated tumor cells (SQ20B) and irradiated normal tissue cells (MRC5). Using gammaH2AX foci at 24 hours after IR, we identified several genes, such as BRCA2, Lig IV, and XRCC5, whose knockdown is known to cause increased cell radiosensitivity, thereby validating the primary screening end point. In addition, we identified POLQ (DNA polymerase ) as a potential tumor-specific target. Subsequent investigations showed that POLQ knockdown resulted in radiosensitization of a panel of tumor cell lines from different primary sites while having little or no effect on normal tissue cell lines. These findings raise the possibility that POLQ inhibition might be used clinically to cause tumor-specific radiosensitization.

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